Back projection visual field tester

ABSTRACT

One embodiment of the present invention is a visual field tester that includes: (a) a projection screen; (b) a stimulus projection system that projects a light stimulus onto a first side of the projection screen; (c) a background projection system that projects a background light onto the first side of the projection screen; and (d) a lens system disposed on a second side of the projection screen that directs light transmitted through the projection screen to a predetermined location.

[0001] This is a continuation-in-part of a patent application entitled“Back Projection Visual Field Tester” having Ser. No. 09/884,507 whichwas filed on Jun. 14, 2001.

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention pertains to an optical apparatus for visualfield testing. In particular, the present invention relates to anoptical apparatus for visual field testing using a back projectionsystem.

BACKGROUND OF THE INVENTION

[0003] A visual field tester is an apparatus that is used to test, amongother things, the peripheral vision of a human eye—such an apparatus hasbeen known in the art for many years. Test results from visual fieldtesters are used to diagnosis diseases that cause degradation of visionsensitivity. For example, a Standard Automated Perimeter (SAP), one ofthe most accepted of such testing apparatus, typically performsbrightness contrast sensitivity tests over a large visual field.

[0004] In prior art visual field testers used to perform a contrastsensitivity test, it is common to include a hemispherical projectionsurface and a stimulus optical projection system. In a typical suchvisual field tester, the hemispherical projection surface is uniformlyilluminated (for example, using a white light source) to provide aconstant and uniform background illumination—the aim is that thehemispherical projection surface be a Lambertian illumination surface(i.e., a surface upon which brightness is constant over differentviewing angles). In a typical such visual field tester, the stimulusoptical projection system presents stimuli (typically in the form of acircular spot) at selected points on an internal surface of thehemispherical projection surface. For example, this is done bysequentially flashing images of light sources on the internal surface ofthe hemispherical projection surface where the position and brightnessof the stimuli are specified by a computer implemented algorithm. In usefor testing, a patient's eye is placed at, or close, to a center of asurface of a volume enclosed by the hemispherical projection surface,and the patient is asked to respond to the stimuli by pressing, forexample, a mouse button. Then, the contrast sensitivity of the patient'svisual field is mapped by changing the brightness and position of thestimuli on the constant, uniform background illumination, and recordingthe patient's response thereto. However, such prior art devices have adrawback in that they are bulky and expensive. In particular, the radiusof the hemispherical projection surface is typically set to about 30 cmto enable the patient to see the stimulus comfortably (i.e., withoutstraining the patient's test eye).

[0005] U.S. Pat. No. 5,870,169 (the '169 patent) discloses a visualfield tester that utilizes a hemispherical surface in an alternativemanner to that described above. Specifically, instead of projecting astimulus onto an internal surface of a hemispherical projection surfacefrom the patient's side, as disclosed in the '169 patent, a rearprojection device is used to project a stimulus onto an external surfaceof a hemispherical projection surface. In this case, the hemisphericalprojection surface is comprised of a transparent material, and thepatient can see the stimulus when it is viewed from the interior surfaceof the hemispherical projection surface. The apparatus in the '169patent provides a stimulus having an improved shape and brightnessuniformity over the apparatus's 72-degree visual field when comparedwith the shape and brightness uniformity of prior visual field testers.Since there are moving mechanisms on the back of the projection surface,the background illumination is provided from the front side of theprojection surface. Therefore, the projection surface has to be coatedwith an absorbing material to reflect the background illumination fromthe front side. However, due to absorption by the absorbing material,the maximum brightness of the stimulus is reduced.

[0006] Another visual field tester is disclosed in U.S. Pat. No.5,046,835 (the '835 patent). As disclosed in the '835 patent, the sizeof a visual field tester can be reduced by using a cupola-less opticalsystem. In particular, the '835 patent discloses a direct viewingoptical system that projects a stimulus directly into a patient's eye.To do this, the optical system images a light source onto anintermediate image plane of an eyepiece (to serve as a stimulus), andseparately images light output from a diffused light source onto theintermediate image plane (to serve as a uniformly illuminatedbackground). Then, the stimulus and the background are combined througha beamsplitter, and projected onto the patient's retina. In use, thepatient views a test field through large field of view (60 degrees),long working-distance eyepieces. Because the apparatus disclosed in the'835 patent does not utilize a hemispherical projection surface, thesize of the apparatus is significantly reduced. However, the cost of alarge field of view, long working-distance eyepiece is increased due theaperture size of the lens.

[0007] U.S. Pat. No. 6,139,150 discloses a visual field tester that usesa retro-reflector array to eliminate use of an eyepiece. As a result,the visual field tester has reduced cost and complexity when comparedwith the above-described apparatus. However, it is difficult tomanufacture a retro-reflector array having a quality that is as high asis required to perform a visual field test.

[0008] In light of the above, there is a need in the art for furthervisual field testers that can, for example, provide an SAP test in acost-effective way.

SUMMARY OF THE INVENTION

[0009] One or more embodiments of the present invention advantageouslysatisfy the above-identified need in the art, and provide a backprojection visual field tester. Specifically, one embodiment of thepresent invention is a visual field tester of a patient's eye thatcomprises: (a) a projection screen; (b) a stimulus projection systemthat projects a light stimulus onto a first side of the projectionscreen; (c) a background projection system that projects a backgroundlight onto the first side of the projection screen; and (d) a lenssystem disposed on a second side of the projection screen that directslight transmitted through the projection screen to the patient's eye.

BRIEF DESCRIPTION OF THE FIGURE

[0010]FIG. 1A shows a block diagram of one embodiment of a backprojection visual field tester that is fabricated in accordance with thepresent invention;

[0011]FIG. 1B shows a block diagram of an alternative embodiment of astimulus projection system that can be utilized to fabricate a backprojection visual field tester in accordance with one or moreembodiments of the present invention;

[0012]FIG. 1C shows a block diagram of alternative embodiments of astimulus projection system that can be utilized to fabricate a backprojection visual field tester in accordance with one or moreembodiments of the present invention;

[0013]FIG. 2 shows a block diagram of an alternative embodiment of abackground illumination system that can be utilized to fabricate a backprojection visual field tester in accordance with one or moreembodiments of the present invention;

[0014]FIG. 3A shows a diagram of one embodiment of a projection screenthat can be utilized to fabricate a back projection visual field testerin accordance with one or more embodiments of the present invention;

[0015]FIG. 3B shows a diagram of an alternative embodiment of aprojection screen that can be utilized to fabricate a back projectionvisual field tester in accordance with one or more embodiments of thepresent invention;

[0016]FIG. 4 shows a block diagram of an alternative embodiment of astimulus viewing system that can be utilized to fabricate one or moreembodiments of the present invention;

[0017]FIG. 5 shows a block diagram of an alternative embodiment of astimulus projection system and a background illumination system that canbe utilized to fabricate a back projection visual field tester inaccordance with one or more embodiments of the present invention;

[0018]FIG. 6 shows a diagram of a front view of a portion of thestimulus projection system and background illumination system shown inFIG. 5; and

[0019]FIG. 7 shows a block diagram of an alternative embodiment of alight monitoring optical system that can be utilized to fabricate a backprojection visual field tester in accordance with one or moreembodiments of the present invention.

DETAILED DESCRIPTION

[0020]FIG. 1A shows a block diagram of back projection visual fieldtester 100 that is fabricated in accordance with one embodiment of thepresent invention. As shown in FIG. 1A, a stimulus projection system forback projection visual field tester 100 comprises light source 101 andstimulus projection lens system 102 (those of ordinary skill in the artwill readily understand that stimulus projection lens system 102 maycomprise one or more lenses). In use, an aperture (not shown) of lightsource 101 is imaged by stimulus projection lens system 102 ontoprojection screen 105 (embodiments of projection screen 105 will bedescribed below in conjunction with FIGS. 3A and 3B) to provide astimulus (in FIG. 1A, the stimulus is shown at various positions asstimuli 104 to illustrate that the stimulus may be presented to apatient at various positions on projection screen 105). Light source 101may include an LED, a Halogen lamp, a short arc Mercury lamp, a Xenonlamp, a laser, or any other suitable light source. The shape of thestimulus may be circular (a typical visual field tester utilizes acircular spot), or it may be any other shape, which shape can beprovided by utilizing an aperture for light source 101 in accordancewith any one of a number of methods and apparatus that are well known tothose of ordinary skill in the art. Further, the shape of the stimulusmay be changed under the control of controller 150 (for example, acomputer such as a PC) by changing the aperture and/or its shape inaccordance with any one of a number of methods and apparatus that arewell known to those of ordinary skill in the art. Still further, aninterface apparatus (not shown) is disposed between controller 150 andlight source 101 in a manner which is well known to those of ordinaryskill in the art. Then, in accordance with methods that are well knownto those of ordinary skill in the art, for example, under softwarecontrol, controller 150 sends signals through the interface apparatus tolight source 101 to cause it to emit light. In accordance with methodsthat are well known to those of ordinary skill in the art, controller150, under software control, controls output from light source 101 as toone or more of: (a) duration of an illumination interval; (b) intensityof illumination during the illumination interval; and (c) color. Forexample, color may be controlled by use of filters in a manner that iswell known to those of ordinary skill in the art. Further, the controlinput for controller 150 can result from predetermined criteria and/orfrom user input by means of a user interface (not shown) in accordancewith any one of a number of methods that are well known to those ofordinary skill in the art.

[0021] As further shown in FIG. 1A, beamsplitter 109 is disposed in anoptical path of the stimulus projection system, and beamsplitter 109directs a portion of the light output from light source 101 tophotodetector 110. Output from photodetector 109 is applied as input tocontroller 150, and controller 150 utilizes this input to monitor, amongother things, the brightness of the stimulus. Many methods and apparatusare well known to those of ordinary skill in the art for fabricatingbeamsplitter 109 and photodetector 110.

[0022] As further shown in FIG. 1A, light passing through beamsplitter109 impinges upon scanner system 103, and is directed by scanner system103 to impinge on projection screen 105 at various positions across thesurface thereof. An interface apparatus (not shown) is disposed betweencontroller 150 and scanner system 103 in a manner that is well known tothose of ordinary skill in the art. Then, in accordance with methodsthat are well known to those of ordinary skill in the art, for example,under software control, controller 150 sends signals through theinterface apparatus to scanner system 103 to cause scanner system 103 tomove and, thereby, to scan the light incident thereon over the surfaceof projection screen 105. As shown in FIG. 1A, scanner system 103comprises gimbal-mounted, turning mirror 103. Many methods are wellknown to those of ordinary skill in the art for use in fabricating acontroller-controlled scanner, and in particular, acontroller-controlled, gimbal-mounted, turning mirror. For example, asuitable gimbal-mounted, turning mirror apparatus is manufactured by theNewport Corporation of Irvine California.

[0023] Since back projection field tester 100 shown in FIG. 1A utilizesgimbal-mounted, turning mirror 103 to move the stimulus to variouspositions on projection screen 105 to provide stimuli 104, stimuli 104will be focused over a spherical surface whose radius is determined bymovement of turning mirror 103. As a result, the depth of focus ofstimulus projection lens system 102 should be designed to be largeenough so that stimuli 104 are substantially in focus over the usefulscan rage. Thus, the numerical aperture of stimulus projection lenssystem 102 should be small enough to provide the desired depth of field.

[0024] Embodiments of the present invention are not limited to the useof a gimbal-mounted, turning mirror. For example, instead of usinggimbal-mounted, turning mirror 103 to control the position of thestimulus (see stimuli 104 in FIG. 1A), alternative embodiments of thepresent invention can be fabricated using a translation apparatus thatmoves a stimulus producing light beam over a surface (for example, aplane) that is substantially parallel to a back surface of projectionscreen 105. FIG. 1B shows a block diagram of stimulus projection system131 that is mounted on a mechanical arm (not shown), which stimulusprojection system 131 can be moved (in response to input signals from acontroller) in a plane parallel to projection screen 105 in either X-Ycoordinates (indicated by arrows 156), or in polar coordinates. Manymethods and apparatus are well known to those of ordinary skill in theart for use in fabricating a controller-controlled mechanism that canprovide such motion in a plane. For example, it is well known how toprovide an X-Y type motion in a plane like a plotter device utilizing,for example, a pair of motors (one motor for providing motion along anX-axis, and one motor for providing motion along a Y-axis). In addition,it is well known in the art how to provide a polar coordinate typemotion in a plane utilizing, for example, two motors, a rotation armapparatus, and a carrier that travels on the rotation arm apparatus (onemotor for providing rotation of the rotation arm apparatus, and onemotor for providing motion of the carrier along the rotation armapparatus). Stimulus projection system 131 comprises a light source, forexample, like light source 101 described above in conjunction with FIG.1A, and a projection lens system.

[0025] Advantageously, in accordance with such an embodiment, thedistance between stimulus projection system 131 and projection screen105 will be substantially the same distance as stimulus projectionsystem 131 is moved. As a result, the depth of focus of the projectionlens system comprising stimulus projection system 131 can have a depthof focus that is smaller than that of projection lens system 102 of FIG.1A. Thus, the numerical aperture of the projection lens system can beincreased to increase the brightness of the stimulus produced bystimulus projection system 131.

[0026] In accordance with a further aspect of the embodiment shown inFIG. 1B, stimulus projection system 131 is mounted on a furthermechanical arm (not shown) to provide a tilting mechanism. In accordancewith this further aspect, the further mechanical arm can move (inresponse to input signals from a controller) in a direction causes lightoutput from stimulus projection system 131 to be directed toward thecenter of magnifier lens 107 (see FIG. 1A) of the stimulus viewingsystem. Such a tilting mechanism can be used when stimulus projectionsystem 131 is mounted to move in X-Y coordinates or when it is mountedon a rotation arm to move in polar coordinates. In accordance with thisfurther aspect, varying the tilt angle can advantageously compensate forbrightness differences that might occur when stimulus projection system131 is moved to various locations over a surface that is substantiallyparallel to a back surface of projection screen 105. For example,without varying the tilt angle, the brightness of the stimulus, asperceived by the test eye, may be different when the position of thestimulus changes from a central position on projection screen 105 to aperipheral position on projection screen 105. In fabricating anembodiment in accordance with this further aspect, the depth of focus ofthe projection lens system should be designed to be large enough toaccount for differences in distance between stimulus projection system131 and projection screen 105 caused by differences in tilt angle atdifferent positions of stimulus projection system 131 (advantageously,this will ensure that the stimulus is in focus when stimulus projectionsystem 131 is moved to the different positions).

[0027]FIG. 1C shows a block diagram of stimulus projection system 220that is fabricated in accordance with an alternative embodiment of thepresent invention. Stimulus projection system 220 may replace a portionof the stimulus projection system comprised of light source 101 andstimulus projection lens system 102 shown in FIG. 1A, or it may serve asstimulus projection system 131 shown in FIG. 1B. As shown in FIG. 1C,bright, white light source 200 (such as, for example, an arc lamp, aHalogen lamp, or any one of a number of other light sources that arewell known to those of ordinary skill in the art) outputs light that iscoupled into optical fiber 201, and light output from optical fiber 201is transmitted, in turn, by stimulus projection lens system 202 tolocation 230 to form a stimulus. Although stimulus projection lenssystem 202 is shown as being comprised of one lens, those of ordinaryskill in the art will readily understand that stimulation projectionlens system 202 may comprise one or more lenses. In an alternativeembodiment, stimulus projection system 220 may comprise white LED 210(or other small emitting area light sources that are well known to thoseof ordinary skill in the art), condensing lens system 211, and aperture212 to form a stimulus in place of bright, white light source 200 andoptical fiber 201. For this alternative embodiment, light emanating fromaperture 212 is transmitted by stimulus projection lens system 202 tolocation 230 to form a stimulus.

[0028] For embodiments of the present invention shown in FIG. 1C thatare utilized, for example, with a turning mirror (like gimbal-mounted,turning mirror 103 shown in FIG. 1A) to move the stimulus overprojection screen 105, stimulus projection lens system 202 is preferablydesigned to have such a long depth of focus that the image of a lightaperture (for example, the image of optical fiber 201 or the image ofaperture 212), and, thereby, the stimulus, is well focused over theentire area of projection screen 105. To do this, in accordance with oneembodiment of the present invention, one designs stimulus projectionlens system 202 (in accordance with any one of a number of methods thatare well known to those of ordinary skill in the art) to have anumerical aperture (i.e., as shown in FIG. 1C, the angle subtended fromlocation 230 to stimulus projection lens system 202) that is smallenough to achieve the desired long depth of focus. However, embodimentsof the present invention shown in FIG. 1C that are utilized withembodiments of the present invention that are fabricated in accordancewith a teaching described above in conjunction with FIG. 1B, may beadvantageously used without a stimulus projection lens system having along depth of focus.

[0029] Referring back to FIG. 1A, light source 106 substantiallyuniformly illuminates projection screen 105 with light. Light source 106may comprise LEDs, tungsten lamps, Halogen lamps, a fluorescent lamp,and so forth. For example, in some embodiments, light source 106 maycomprise a number of light sources, and in other embodiments it maycomprise a light source in the form of, for example, a ring. Inaddition, in accordance with one embodiment, an interface apparatus (notshown) is disposed between controller 150 and light source 106 in amanner which is well known to those of ordinary skill in the art. Then,in accordance with methods that are well known to those of ordinaryskill in the art, for example, under software control, controller 150sends signals through the interface apparatus to light source 106 tocause it to emit light. In accordance with methods that are well knownto those of ordinary skill in the art, controller 150, under softwarecontrol, controls output from light source 106 as to one or more of: (a)duration of an illumination interval; (b) intensity of illuminationduring the illumination interval; and (c) color. For example, color maybe controlled by use of filters in a manner that is well known to thoseof ordinary skill in the art. Further, the control input for controller150 can result from predetermined criteria and/or from user input bymeans of a user interface (not shown) in accordance with any one of anumber of methods that are well known to those of ordinary skill in theart.

[0030] In accordance with further embodiments of the present invention,blue filters can be placed in the optical path of the stimulusprojection system to generate a blue stimulus; and backgroundillumination light source 106 can be either a yellow LED or a whitelight source covered with a yellow filter to generate a desired yellowbackground for a short-wavelength, standard automatic perimeter (SWAP)test.

[0031]FIG. 2 shows a block diagram of an alternative embodiment of abackground illumination system that can be utilized to fabricate a backprojection visual field tester in accordance with one or moreembodiments of the present invention. As shown in FIG. 2, light source106 directs light at walls 120 of an enclosure of a back of projectionscreen 105. In one such embodiment, walls 120 of the enclosure have awhite, rough surface which serves, as shown in FIG. 2, as an integratingsphere to provide uniform background illumination for projection screen105. Many other method and apparatus are well known to those of ordinaryskill in the art for providing such a result. In using such embodiments,projection screen 105 is: (a) substantially uniformly illuminated bylight from light source 106 and walls 120; and (b) illuminated bystimuli 104 generated by the stimulus projection system comprised oflight source 101, stimulus projection lens system 102, and turningmirror 103 where one or more of: (i) duration of an illuminationinterval; (ii) intensity of illumination during the illuminationinterval; and (iii) color are determined by, for example, controller 150in accordance with predetermined criteria and/or in response to userinput. In addition, one or more of: (a) duration of an illuminationinterval; (b) intensity of illumination during the illuminationinterval; and (c) color of light source 106 are determined by, forexample, controller 150 in accordance with predetermined criteria and/orin response to user input.

[0032] Referring back to FIG. 1A, projection screen 105 is viewedthrough a stimulus viewing system by a patient whose test eye is locatedat position 108. Position 108 is substantially at a center of a viewingbox (not shown) which is, for example, a cone shaped enclosure. As shownin FIG. 1A, the stimulus viewing system for back projection visual fieldtester 100 comprises magnifier lens system 107 (those of ordinary skillin the art will readily understand that magnifier lens system 107 maycomprise one or more lenses).

[0033] In accordance with one embodiment of the present invention, thefocal length of magnifier lens system 107 and physical distance 111(i.e., the distance between projection screen 105 and magnifier lenssystem 107) are selected so that projection screen 105 is imaged at adistance about 30 cm away from the patient's test eye to reduce strain.In accordance with such an embodiment, an embodiment of back projectionvisual field tester 100 can be fabricated where the physical distance111 between projection screen 105 and magnifier lens system 107 is muchshorter than the 30 cm distance required for a patient to seecomfortably. Advantageously, this enables the size of projection screen105 and back projection visual field tester 100 to be substantiallyreduced over visual field testers fabricated in accordance with theprior art. To understand the magnitude of such a reduction, assume thatdistance 111 between projection screen 105 and magnifier lens system 107is chosen to be 15 cm. In such a case, the total volume of the viewingoptical space would be only ⅛ of the volume if projection screen 105were physically located 30 cm away from the patient's eye.

[0034] A visual field tester fabricated in accordance with oneembodiment of the present invention may further comprise an apparatusfor providing a fixation target or for fixing the position of apatient's test eye (such apparatus is not shown in FIG. 1A so that theoperation of the remainder of the disclosed back projection visual fieldtester can more easily be understood). Such a fixation apparatus wouldengage the attention of the test eye, and may be fabricated inaccordance with any one of a number of methods that are well known tothose of ordinary skill in the art. For example, a fixation device maybe an LED which is disposed at a predetermined location for viewing bythe patient's test eye. Alternatively, a black dot or a predeterminedpattern, for example and without limitation, a diamond shaped pattern,can be painted on a center of projection screen 105 to serve as afixation target during a central vision test. Further, a pair ofpredetermined fixation patterns can be painted on both horizontal andvertical edges of projection screen 105 to serve as fixation targetsduring a peripheral vision test.

[0035] Lastly, as is well known to those of ordinary skill in the art,in order to fabricate a visual field tester in accordance with thepresent invention, the patient is provided with an apparatus, forexample, indication apparatus 118 in FIG. 1A, for use in indicating apatient's perception of the presence or absence of optical radiationimpinging upon the eye. As is well known, such indication apparatus mayinclude a button which, when depressed, sends a signal to controller150. Such an indication apparatus may also include foot pedals, mouses,and the like. Lastly, controller 150 may be configured in accordancewith any one of a number of methods that are well known to those ofordinary skill in the art to cause the stimuli and the backgroundillumination to be generated in patterns, for example, predeterminedpatterns, suitable to any number of visual tests and to collect thepatient's input to produce, as output, measurements, for example, of thepatient's visual sensitivity.

[0036]FIG. 3A shows a diagram of one embodiment of projection screen 105(shown in FIG. 1A) that can be utilized to fabricate a back projectionvisual field tester in accordance with one or more embodiments of thepresent invention. In accordance with one such embodiment of the presentinvention, projection screen 300 provides two functions. In accordancewith a first function, projection screen 300 (by action of lens 301)acts as a lens or a prism. As such, projection screen 300 (by action oflens 301) directs optical beam 303 (representing light from the stimulusand from the background illumination) towards location 108 (as shown inFIG. 1A) where the patient's test eye is placed. In accordance with asecond function, projection screen 300 (by action of diffuse lightshaper 302) diffuses or expands optical beam 303′ that is output fromprojection screen 300 into a predetermined divergence angle. Becauseprojection screen 300 is transparent, and in a preferred embodiment itis highly transparent (for example, it may be readily fabricated from aplastic material such as polycarbonate, Polyseter, and the like), notmuch light is lost to absorption by the material comprising projectionscreen 105. In accordance with this embodiment of the present invention,the divergence angle of optical beam 303′ is controlled so that opticalbeam 303′ will substantially cover an aperture of magnifier lens system107 (see FIG. 1A). As a result, not much light will be vignetted by theaperture of magnifier lens system 107. Hence, since most of the light isdirected into magnifier lens system 107 and, in turn, the patient's testeye, a high efficiency projection system is achieved. In accordance withone embodiment of the present invention, projection screen 105 can befabricated by physically laminating two optical components together,namely, Fresnel lens 301, and light diffuser 302, each of whichcomponents substantially performs the first and second functionsdescribed above, respectively.

[0037]FIG. 3B shows a diagram of another embodiment of projection screen105 that can be utilized to fabricate a back projection visual fieldtester in accordance with one or more embodiments of the presentinvention. In accordance with this embodiment of the present invention,projection screen 105 can be fabricated by laminating prism array 310and light diffuser 302, each of which components substantially performsthe first and second functions described above, respectively. However,because the prisms in prism array 310 are located at predeterminedpositions, this embodiment can be used for a fixed visual field testpattern wherein light impinges upon the areas of projection screen 105at which the prisms are located.

[0038] As an alternative, projection screen 105 can be fabricated in onesingle piece wherein Fresnel lens 301 or prism array 310 are fabricatedin one side of a screen material such as, for example, and withoutlimitation, acrylic, polycarbonate, and the like. Then, light diffuser302 is fabricated on the other side of the screen material in accordancewith any one of a number of many methods that are well known to those ofordinary skill in the art. For example, light diffuser 302 can be adiffuser having a desired diffusing angle such as a roughened surface,or it can a “holographic diffuser/light shaper” that is manufactured bythe Physical Optics Corporation of Torrance, California. Suchalternative embodiments may be fabricated by forming a mold, and then byreplicating the mold.

[0039] In an embodiment of projector screen 105 where projector screen105 is highly transparent, an object located behind the screen (i.e.,the object is located on a side of the screen opposite from the patient)will be seen by the patient if the object is close to the screen. Infact, the object will be more easily seen if it has high contrast, i.e.,it is black or another color. As those of ordinary skill in the art willappreciate, this is not desirable for a visual field tester. One way ofavoiding this is to design the stimulus projection system, for example,the stimulus projection systems shown in FIGS. 1A, 1B, and 1C, to have along working distance so that the stimulus projection system is farenough from projection screen 105 not to be seen readily. Additionally,the body of the stimulus projection system can also be painted the samecolor as the wall of an enclosure, thereby reducing its contrast whencompared with the background illumination.

[0040]FIG. 4 shows a block diagram of an alternative embodiment of astimulus viewing system that can be utilized to fabricate one or moreembodiments of the present invention. For the most part, stimulusviewing system 400 is the same as the stimulus viewing system shown inFIG. 1A in that it comprises magnifier lens system 107. However, asource of test radiation (for example, a source of infrared radiationthat is fabricated in accordance with any one of a number of methodsthat are well known to those of ordinary skill in the art and is notshown) is directed at a patient's test eye plane 409 (for example, inone embodiment the source of test radiation may be located so that testradiation output from the source is directed to the patient's test eyeplane 409 by reflection from beamsplitter 410). In accordance with oneembodiment, beamsplitter 410 is fabricated in accordance with any one ofa number of methods that are well known to those of ordinary skill inthe art to transmit light such as light from the stimulus and thebackground illumination, and to reflect the test radiation. Testradiation reflected from the patient's test eye passes through magnifierlens system 407, is reflected by beamsplitter 410, passes through filter430, and is imaged to CCD camera 411 by lens system 408 (those ofordinary skill in the art will readily understand that lens system 408may comprise one or more lenses). Filter 430 may be fabricated inaccordance with any one of a number of methods that are well known tothose of ordinary skill in the art to transmit radiation in a band ofwavelengths substantially encompassing wavelengths of the testradiation. For example, filter 430 may be fabricated to transmitinfrared radiation. Filter 430 may be placed in positions other thanthat shown in FIG. 4 and still serve to inhibit passage of radiationother than the test radiation to CCD camera 411. An image output fromCCD camera 411 may be displayed on a video monitor (not shown in FIG. 4)for monitoring purposes. In addition, as has been disclosed in the priorart, CCD camera 411 can also be used as an eye tracking device either byanalyzing a location of the image of the eye in accordance with any oneof a number of methods that are well known to those of ordinary skill inthe art, or by analyzing a reflection of a point light sourceillumination (not shown) in accordance with any one of a number ofmethods that are well known to those of ordinary skill in the art. Thoseof ordinary skill in the art will readily appreciate that CCD camera411, as shown in FIG. 4, can be used with any of the embodimentsdescribed herein.

[0041]FIG. 5 shows a block diagram of an alternative embodiment of astimulus projection system and a background illumination system that canbe utilized to fabricate a back projection visual field tester inaccordance with one or more embodiments of the present invention. FIG. 6shows a front view of a portion of the system. As shown in FIG. 6,projection optics assembly 505 is mounted on disk 507, and projectionoptics assembly 505 is moved by a motor (not shown) in response to inputsignals from a controller in a radial direction in slot 520 disposed indisk 507. As shown in FIG. 5, disk 507 is rotated by a motor (not shown)that is connected to shaft 501 in response to input signals from thecontroller. In this manner, a stimulus is produced by light output fromprojection optics assembly 505 that impinges upon projection screen 502,and the stimulus is moved in polar coordinates (i.e., r, θ).

[0042] As shown in FIG. 5, an interior surface is formed by frontsurface 511 of disk 507, interior surfaces 512 of an enclosure, and aback surface of projection screen 502. The interior surface is made intoa light integrating surface by fabricating front surface 511 of disk507, and interior surfaces 512 of the enclosure to have substantiallythe same color. For example, front surface 511 of disk 507 and interiorsurfaces 512 of the enclosure may all be the same white color. Asfurther shown in FIG. 5, one or more light sources 503 such as, forexample, one or more fluorescent lamps, one or more LEDs, one or moreTungsten lamps, one or more Halogen lamps, and so forth are used toilluminate the light integrating surface. As was the case forembodiments described above, output from projection optics assembly 505and light source 503 is controlled by a controller in a manner like thatdescribed above.

[0043] In accordance with a further aspect of such alternativeembodiments, as shown in FIG. 5, projection optics assembly 505protrudes through an aperture in a strip of material 508 (havingsubstantially the same color as front surface 511 of disk 507). Thestrip of material 508 is wider than slot 520, and is disposed to coverslot 520. Further, strip of material 508 rotates on rollers behind slot520 (the rotation being produced, for example, by the same motor thatcauses movement of projection optics assembly 505) whenever projectionoptics assembly 505 slides along slot 520. As a result, except for alens aperture of projection optics assembly 505, all other surfaces inthe enclosure are fabricated to have substantially the same color asstrip 508 and front surface 511 of disk 507, for example, white, or anyother desired background illumination color for a visual field test.

[0044] In accordance with a still further aspect of such alternativeembodiments, beamsplitter 506 is placed in front of projection opticsassembly 505 to cover the lens aperture of projection optics assembly505. LED 504 outputs light into light integrating cylinder 509 whoseinterior surfaces have the same color as the desired backgroundillumination. Light integrating cylinder 509 homogenizes light outputfrom LED 504, and the homogenized light is reflected by beamsplitter 506to mask the lens aperture of projection optics assembly 505, i.e., thehomogenized light illuminates an area that covers the lens aperture,which area would otherwise be seen by the patient through projectionscreen 502. In addition, in accordance with one embodiment, an interfaceapparatus (not shown) is disposed between a controller and LED 504 in amanner which is well known to those of ordinary skill in the art. Then,in accordance with methods that are well known to those of ordinaryskill in the art, for example, under software control, the controllersends signals through the interface apparatus to LED 504 to cause it toemit light. In accordance with methods that are well known to those ofordinary skill in the art, the controller, under software control,controls output from LED 504 as to one or more of: (a) duration of anillumination interval; (b) intensity of illumination during theillumination interval; and (c) color. For example, color may becontrolled by use of filters in a manner that is well known to those ofordinary skill in the art. Further, the control input for the controllercan result from predetermined criteria and/or from user input by meansof a user interface (not shown) in accordance with any one of a numberof methods that are well known to those of ordinary skill in the art. Bycontrolling the color of light integrating cylinder 509, the brightnessof light output from light integrating cylinder 509, the reflectivity ofbeamsplitter 506 for light output from LED 504, and the transmissivityof beamsplitter 506 for light output from projection optics assembly505, the lens aperture of projection optics assembly 505 may be blendedinto the background illumination. Still further, in accordance with oneembodiment, the brightness of light output from light integratingcylinder 509 can be controlled by using the controller to control theoutput from LED 504.

[0045]FIG. 7 shows a block diagram of an alternative embodiment of alight monitoring optical system that can be utilized to fabricate a backprojection visual field tester in accordance with one or moreembodiments of the present invention. As shown in FIG. 7, stimulusprojection system 720 comprises aperture 703 of a light source (notshown) and projection lens system 702 (those of ordinary skill in theart will readily understand that projection lens system 702 may compriseone or more lenses). Note that aperture 703 is equivalent to aperture212 shown in FIG. 1C, and the light source may comprise light source 210and condenser lens system 211 also shown in FIG. 1C. As further shown inFIG. 7, projection lens system 702 projects light emitted from aperture703 of the light source to stimulus location 704 on a back surface ofprojection screen 701. Those of ordinary skill in the art shouldappreciate that although one embodiment of stimulus projection system720 is shown in FIG. 7 for purposes of illustrating this aspect of thepresent invention, further embodiments of the present invention existwhere stimulus projection system 720 may be fabricated in accordancewith any one of the embodiments described herein.

[0046] As further shown in FIG. 7, light monitoring optical system 710comprises photodetector 705 and image lens system 706 (those of ordinaryskill in the art will readily understand that image lens system 706 maycomprise one or more lenses). In accordance with this embodiment,photodetector 705 is imaged to stimulus location 704 on the back surfaceof projection screen 701. Many methods are well known to those ofordinary skill in the art for coupling stimulus projection system 720and light monitoring optical system 710 so they are imaged to the samelocation on the back surface of projection screen 701. For example, inaccordance with one embodiment, they may be joined together by amechanical arm.

[0047] Output from photodetector 705 may be applied as input to acontroller, for example, controller 150 shown in FIG. 1A, and thecontroller can utilize the input to monitor, among other things, thebrightness of the stimulus. In addition, by using the controller tocontrol intervals when the stimulus is active, the brightness of thebackground illumination (as well as the brightness of the stimulus) atlocation 704 can be measured independently using output fromphotodetector 705. Then, in accordance with one embodiment of thepresent invention, using these measurements of brightness, contrastbetween the stimulus and the background illumination can be controlledaccurately at specific locations on the back surface of projectionscreen 701 by changing one or both the stimulus brightness and thebackground brightness at the specific locations. An advantage of theembodiment shown in FIG. 7 is that use of separate optics paths forstimulus projection system 720 and light monitoring optical system 710avoids issues relating to reflected light that occur when projection andmonitoring optics share the same optical components.

[0048] Those skilled in the art will recognize that the foregoingdescription has been presented for the sake of illustration anddescription only. As such, it is not intended to be exhaustive or tolimit the invention to the precise form disclosed.

What is claimed is:
 1. A visual field tester comprises: a projectionscreen; a stimulus projection system that projects a light stimulus ontoa first side of the projection screen; a background projection systemthat projects a background light onto the first side of the projectionscreen; and a lens system, disposed on a second side of the projectionscreen, that directs light transmitted through the projection screen toa predetermined location.
 2. The visual field tester of claim 1 whereinthe stimulus projection system comprises: a translation apparatus thatis configured to move the stimulus projection system over a surface thatis substantially parallel to a surface of the first side of theprojection screen.
 3. The visual field tester of claim 2 wherein thetranslation apparatus is configured to move the stimulus projectionsystem in X-Y coordinates over a plane.
 4. The visual field tester ofclaim 3 wherein the translation apparatus comprises two motors, onemotor being configured to move the stimulus projection system along theX coordinate and another motor being configured to move the stimulusprojection system along the Y axis.
 5. The visual field tester of claim2 wherein the translation apparatus is configured to move the stimulusprojection system in polar coordinates over a plane.
 6. The visual fieldtester of claim 5 wherein the translation apparatus comprises twomotors, one motor being configured to move the stimulus projectionsystem along a radial polar coordinate and another motor beingconfigured to move the stimulus projection system along an angular polarcoordinate.
 7. The visual field tester of claim 2 which furthercomprises a tilting mechanism that is configured to direct light outputfrom the stimulus projection system at varying angles with respect tothe lens system depending on a position of the stimulus projectionsystem on the surface.
 8. The visual field tester of claim 1 wherein thebackground projection system comprises a source disposed in an enclosurethat is configured to function substantially as a light integratingsphere.
 9. The visual field tester of claim 8 wherein the enclosurecomprises walls having a white, rough surface.
 10. The visual fieldtester of claim 1 wherein the projection screen comprises: a prismarray; and a diffuser element.
 11. The visual field tester of claim 1wherein the projection screen comprises: a Fresnel lens; and a lightshaping diffuser element.
 12. The visual field tester of claim 1 whichfurther comprises: a beamsplitter disposed between the projection screenand the lens system; a source of test radiation whose output is directedtoward the predetermined position; a lens group configured to relayreflected test radiation, which reflected test radiation light isreflected from a patient's eye disposed at the predetermined location;and a CCD camera disposed to collect the relayed test radiation.
 13. Thevisual field tester of claim 12 that further comprises a monitor thatdisplays an image output from the CCD camera.
 14. The visual fieldtester of claim 12 wherein the source of test radiation is a source ofinfrared radiation and wherein the visual field tester further comprisesa filter disposed to transmit the reflected test radiation and blockradiation having wavelengths of the light transmitted through theprojection screen.
 15. The visual field tester of claim 1 wherein: thestimulus projection system comprises a disk having a slot and a stimulussource of light and a projection lens system configured to move in theslot; and the background projection system comprises an enclosure havingwalls and a source of the background light disposed therein, wherein asurface of the disk forms a portion of a surface of the enclosure. 16.The visual field tester of claim 15 wherein the surface of the disk, andsurfaces of walls of the enclosure are substantially the same color. 17.The visual field tester of claim 16 wherein the stimulus projectionsystem further comprises a strip of material that is wider than the slotand that moves as the source and projection lens move to provide abacking for the slot.
 18. The visual field tester of claim 15 whereinthe stimulus projection system further comprises a radiation sourceconfigured to output radiation that masks a lens aperture of thestimulus projection system.
 19. The visual field tester of claim 18wherein the radiation source comprises a masking source disposed in anintegrating enclosure, and a beamsplitter disposed over the lensaperture that is configured to direct the radiation output from theintegrating enclosure toward the projection screen, and to transmitlight output from the stimulus source of light.
 20. The visual fieldtester of claim 1 which further comprises: a photodetector disposed todetect light reflected from a location on the first side of theprojection screen.
 21. The visual field tester of claim 20 which furthercomprises a controller that controls the stimulus projection system, andthe background projection system, and is responsive to output from thephotodetector.
 22. The visual field tester of claim 21 wherein thecontroller causes the photodetector to detect light reflected from thelight stimulus at the location.
 23. The visual field tester of claim 21wherein the controller causes the photodetector to detect lightreflected form the background light at the location.